The present invention relates to a series regulator and more particularly to a series regulator that has an over current protection circuit.
Series regulators are used in electronic circuits and devices to provide a relatively stable DC (Direct Current) output voltage with limited fluctuation to a large variation in load current. Such regulators are also known as Low Drop Out (LDO) regulators. Typically, LDO regulators rely on a feedback voltage to maintain a constant output voltage. More specifically, an error signal whose value is a function of the difference between the feedback voltage (proportional to the actual output voltage) and a nominal value is amplified and used to control current flow through a pass device such as a power transistor, from the power supply to the load. LDOs are especially beneficial for limiting unnecessary supply power drain in portable battery-powered devices such as cameras, laptop computers, cellular telephones, personal digital assistants and handheld entertainment devices.
Over-current protection is typically required when unusually low resistances or a short-circuit condition occurs in the output of a regulator circuit. Over-current protection can be achieved by employing a circuit that monitors the current delivered to a load and then clamping the current when it exceeds a predetermined maximum level. Such circuits may require floating currents or at least one reference current that is greater than the bias current of the rest of the regulator.
For small, battery-powered devices, it is important to conserve the charge in the battery. Thus, there is a need for a series regulator that does not require large reference currents or a have floating current, and can limit current drain when at or near a short circuit load condition.